The determination of the location of the involutes is usually very uncomplicated with symmetrical spur gears. The position of the right flank and of the left flank is determined at a point and the path between these points is subsequently halved. This calculated point lies on the bisectrix at the center of the tooth gap. The purpose of this process is the determination of the optimum gap center.
There are different processes in accordance with the prior art for determining the tooth flank positions depending on whether the flank position is to be recognized contactlessly or by contact. In contact sensing processes, contact sensing devices are used or the tooth flank is contacted by the respective machining tool and the contact between the tool and the workpiece is determined via different recognition mechanisms.
There are various processes for convergence between the tool and the tooth flank depending on whether the tool is a disk-shaped or a worm-shaped tool. With disk-shaped tools, it is sufficient if, e.g. the workpiece is rotated for so long clockwise or counter clockwise until the contact between the tooth flank of the workpiece and the tool is established. Alternatively to this, the tool can be displaced in parallel with its axis.
With worm-shaped or gear-shaped tools, the tool is frequently rotated for so long until a contact is recognized. The workpiece can here also additionally be rotated or the tool can be displaced in parallel with its axis. Since the axes all have measurement systems, the axis positions on the contact between the workpiece and the tool can be determined exactly and the respective positions with respect to one another can be calculated.
It must be considered with worm-shaped tools whether the tool has a closed generating cut contour as with a grinding worm or whether it is, e.g., a hob in which only the tool edge has the contour relevant to the process. A contour deviating therefrom is then present between these two edges. If the contact is established at such a surface between the workpiece and the tool, the measured result can only be used with restrictions.
With conventional spur gear teeth in which the tooth flanks are symmetrical, this position determination is sufficient for normal machining operations. If in contrast the tooth flanks differ considerably between the right tooth flank and the left tooth flank and/or if the tooth flanks are also designed conically over the tooth width for this purpose, an averaging between two measurement points is no longer sufficient to describe the location of the involutes or an incorrect position may result from this.
This positioning is, however, necessary to be able to further machine pre-gear-cut workpieces. This is the case, on the one hand, when workpieces were pre-gear-cut in the soft state and now are also to be finished after a heat treatment in the hardened state as is the case, for example, with a gear-cutting grinding process and/or a gear-cutting honing process.
The shape of the deformations over the tooth width caused by the heat treatment process is frequently also relevant in addition to the location of the gear on the postmachining in the hardened state. In this case, the location of the gear has to be determined in a plurality of planes in relation to the tooth width. This is above all not very simple with very conical and/or asymmetrical gears.
In tooth grinding processes and tooth honing processes, an attempt is above all also made to keep the machining allowance as small as possible in the soft machining. It is additionally important here after the heat treatment also to determine the allowance distribution over the periphery of the gear in addition to the hard deformations so that too much material is not removed at some points of the gear and the tooth flank is subsequently soft again in these regions. This could result in transmission damage in the assembled transmission under working conditions and thus in a premature end of the transmission service life.
There are furthermore applications in which a second gear has to be machined or manufactured in dependence on a first gear. An exact knowledge of the location of the first gear is also absolutely necessary in this case.
A further application is the machining of rough-forged or sintered blanks. They are typically also postmachined to increase the gear accuracy. For this purpose, the position of the tooth gaps or of the teeth to be post-worked likewise has to be known with sufficient accuracy so that the machining allowance can be selected as low as possible in the premachining.
The object of the present disclosure deals with the further development of current measurement processes for the location determination of the involutes of a gear wheel so that they in particular also deliver sufficiently accurate measured results with gear wheels having an asymmetrical and/or conical flank shape.
This object is achieved by the method in accordance with the features of claim 1. Advantageous embodiments of the method are the subject of the subordinate claims dependent on the main claim.
In accordance with claim 1, a method is proposed for the location determination of the involutes of a pre-gear-cut workpiece within a gear cutting machine using a toothed tool.
The processes known from the prior art for the centering of gears are suitable for symmetrically toothed workpieces. As soon as a workpiece or tool having an asymmetrical or conical flank shape is used, such processes deliver erroneous results. A further developed method is therefore proposed in accordance with the present disclosure which takes account of the geometrical properties of asymmetrical and/or conical gears and calculates the location determination of the involutes based thereon.
In the method in accordance with the present disclosure, the tool and the workpiece form a helical rolling type gear transmission of two outer gears or of one outer gear and one inner gear. The workpiece and/or the tool can have both an asymmetrical cylindrical gear and a conical gear (beveloid gear). The workpiece is preferably a gear wheel having conical and/or asymmetrical spur gear teeth.
Possible manufacturing processes in which the method in accordance with the present disclosure for the location determination of the involutes can be used are, for example, gear grinding, hobbing, skiving hobbing, scraping, skiving and inside and outside honing, wherein both cylindrical and concical tools can be used in all these processes.
The method in accordance with the present disclosure admittedly primarily serves the location determination of the involutes in asymmetrical and/or conical gears, but the method can also easily be used with symmetrical cylindrical gears of the workpiece and/or of the tool. The subject matter of the present disclosure should therefore not be restricted to being carried out with asymmetrical cylindrical and/or conical gears.
It must furthermore be noted that the carrying out of the method steps in accordance with the present disclosure is based on an interaction between the tool and the workpiece. The location of the involutes can be determined both at the workpiece and alternatively at the tool using the method. For reasons of simplicity, only the location determination at the workpiece will be addressed in the following.
The core idea in accordance with the present disclosure is based on the interaction of the two gears. There is the also the possibility against this background to replace the workpiece or the tool with a so-called master wheel whose dimensions are known and which serves the location determination of the involutes of the gear wheel pair (workpiece or tool).
The method in accordance with the present disclosure comprises the following method steps:
a. Generating a first relative movement between the workpiece and the tool; detecting the resulting first contact between a first tooth flank, preferably the left tooth flank, of the tool and a first tooth flank, preferably the left tooth flank, of the workpiece; and detecting a first set of coordinates for representing the relative movement of the workpiece and the tool;b. Generating a second relative movement between the workpiece and the tool; detecting the resulting second contact between a second tooth flank, preferably the right tooth flank, of the tool and a second tooth flank, preferably the right tooth flank, of the workpiece; and detecting a second set of coordinates for representing the relative movement of the workpiece and the tool;c. Determining the angles of rotation, the feeds, the axial distance and the crossed-axes angle of the tool and the workpiece based on the first and second sets of coordinates; and calculating the location of the involutes on the basis of the angles of rotation, the feeds, the axial distance and the crossed-axes angle.
Different methods such as are already known from the prior art can be used for detecting the contact between two tooth flank pairs. For example, the recognition of a contact can take place by measuring at least one motor value of the actuator drives of the gear cutting machine. The motor current, the motor voltage, the motor torque, the motor speed or the effective motor power of one of the actuating drives of the gear-cutting machine have proven themselves as suitable motor values. The contact can be determined, for example, at the measured signal progression of at least one of the named motor values.
Which machine axis of the tool and/or of the workpiece generates the relative movement to achieve the contact between the two gears is of no significance for the carrying out of the method in accordance with the present disclosure. All available machine axes could theoretically be used together, only some of the available axes or only a single one. It is only essential for the carrying out of the method that the two gears of the workpiece and the tool are in contact at their involute surfaces.
Provided both gears mesh with one another, this contact can easily take place while the helical rolling type gear transmission rotates with roller coupling and the contact is achieved by opening the coupling with any desired axis suitable for this purpose.
The method in accordance with the present disclosure can, however, preferably also be carried out when the gears of the workpiece and the tool do not mesh with one another. In this case, a roller-coupled rotation of the transmission is only possible about a small angle since there is otherwise a risk of collisions with other teeth. The contact thus so-to-say has to take place at a standstill.
Position values for describing the relative location of the workpiece and tool at the moment of the contact can be determined with the aid of the recorded sets of coordinates for the contact of the left and right tooth flank pairs. The position values preferably form all degrees of freedom of the tool and workpiece clamped in the machine. The angle of rotation of the workpiece and the tool, the feed, for example the axial feed, of the workpiece and the tool, and their axial distance and their crossed-axes angle count as position values. These position values are determined both for the contact of the left tooth flank pair and the right tooth flank pair. With knowledge of these values, the location of the involute on the right tooth flank and on the left tooth flank can be calculated, i.e. the base gap half-angle for the right flank and for the left flank at a defined reference direction.
Only the sum of the two base gap half-angles of the left and right flanks is unambiguous for an asymmetrical gear. The values for the respective angles depend on the reference direction of the gap, which can be selected as desired, in a reference transverse section plane, which can be selected as desired.
It is a requirement for the direct calculation of the left and/or right base gap half-angle(s) that the locations of the left and right involutes of the tool are known.
It is a requirement for the direction calculation of the difference of the base gap half angle (Δηb) that the difference of the base gap half-angles of the tool is known.
The relative location of the two gears with respect to one another can preferably be described on the basis of so-called kinematic chains from which the above-named position values result. Different kinematic chains exist depending on the gear type of the workpiece and/or of the tool. Such kinematic chains in particular form all six spatial degrees of freedom of the workpiece and/or of the tool.
Values which describe the location and position of the individual machine axes serve as the first and/or second set/sets of coordinates. Corresponding measurement values are stored after every contact. The physical machine axes of the gear-cutting machine are, however, not necessarily covered by the degrees of freedom of the kinematic chains. For the case that all the degrees of freedom cannot be mapped by machine axes, it is advantageous if the desired position values can be determined by equating the matching kinematic chain with a transformation of the detected machine coordinates. It is in particular conceivable in this connection that the angles of rotation, the feeds or the axial feeds, the axial distance and the crossed-axes angle are determined by equating a kinematic chain with the transformation of the recorded sets of coordinates.
It is a requirement for the direct calculation of the left and/right base gap half-angle(s) that the locations of the left and right involutes of the gear wheel pair, i.e. of the tool, are known. The locations of the left and right involutes of the workpiece then have to be known for the converse case for the measurement of the tool.
It is sufficient for the calculation of the relative location of the left and right tooth flanks of the tool if the sum of the left and right base gap half-angles of the tool is known, i.e. if the tooth thickness of the tool teeth is known. This information is sufficient to calculate the sum of the base gap half-angles of the workpiece, i.e. the tooth thickness of the workpiece tooth.
There is the risk that the result of the location determination of the involutes is falsified when one or both of the gears of the workpiece or tool are modified. Such modifications can, for example, occur on the workpiece by the pre-gear-cutting process, by distortion due to hardening and/or by preceding machining steps/machining strokes with modified tools. They occur in tools, for example, due to wear defects or production defects and/or are deliberately placed into the tool to generate modifications directly on the workpiece. If these modifications are already known, they can be taken into account in the location determination of the involutes. The correction can be applied, for example, to both gears and to only one gear.
There is the possibility in an advantageous embodiment of the present disclosure that the calculated location of the involutes is used to center the tool for the following gear-cutting process with respect to the workpiece. This process was previously only possible in an automated manner for symmetrically cylindrical gears. The centering process can also be carried out in the gear-cutting machine fully automated on the basis of the method in accordance with the present disclosure with asymmetrical cylindrical and/or conical gears.
It is considered sufficient in the method in accordance with the present disclosure to contact exactly one left flank and one right flank. The location of the involutes can already be calculated directly after one measurement pass. To reduce effects due to measurement inaccuracies or profile deviations, it may be sensible to repeat the measurements with identical contact points and/or with different contact points, i.e. with different axial positions and/or at different tooth gaps/teeth/pitches of the tool and/or of the workpiece and to statistically evaluate the measured values to reduce measurement inaccuracies. Alternatively or additionally, the high number of measurement repeats can also be used for an allowance analysis and/or measurement of profile/flank and/or for a pitch measurement and/or a tooth thickness measurement.
The preceding allowance analysis can be considered for the centering, for example, to center the tool for the following gear-cutting machining such that the stock removal on the left flank and on the right flank of the workpiece is identical or almost identical in the normal direction. A stock removal ratio from the left and right flank sides of approximately 40 to 60% or less is considered approximately identical. It is moreover also possible to set the removal ratio from left and right directly as desired.
The method in accordance with the present disclosure can be used both for tools having an undefined edge, i.e. for workpieces in which the envelope gear corresponds to the geometry of the tool and for tools having a defined edge with an envelope gear differing from the geometry of the tool. An example for tools having an undefined edge is a grinding worm, for example, etc. In contrast, a hob represents a tool having a defined edge.
Hobs are therefore frequently premeasured externally to obtain information on where the tool edges lie relative to the hob periphery and to a reference surface at the tool mount. For the measuring procedure in accordance with the present disclosure, the hob can then be used in a positioned manner and a contact between the tool blade and the workpiece can be directly achieved for the location determination of the involutes. It therefore has to be ensured for the carrying out of the method that the contact points between the workpiece and the tool arise on the tool edge. This requirements is ensured, for example, in that movement axes of the tool and/or of the workpiece, preferably the angle of rotation and/or the feed of the tool and/or of the workpiece, are aligned in advance with knowledge of the location of one or more lands of the tool so that the contact point(s) between the workpiece and the tool lie(s) in the region of a defined edge, i.e. on the envelope gear of the tool.
The carrying out of the method can in particular be problematic in the location determination or in the centering of tools having narrow gears and unfavorable contact conditions. If, for example, one of the gears is so narrow that the theoretical distance of the contact points in the z direction is larger on the left and right flanks than the width of the tooth, the contact points on the left and right flanks on the narrow gears cannot arise on the involute. A contact with the edge of the gear takes place and a precise centering is no longer possible. It is proposed for this special case in the method in accordance with the present disclosure either to move more than one of the axes for the angle of rotation and the feed of the tool and/or tool between the contacts on the left and right flanks or to carry out a pivot movement in addition to one of these named axes to change the crossed-axes angle.
The method described in this present disclosure for determining the location of the involutes of a workpiece is not always carried out for every workpiece of one type prior to machining. It is typically carried out once or a few times for a workpiece of one type, in particular in mass production. An insertion sensor can then be taught with the result of this location determination in accordance with a preferred embodiment of the present disclosure. Such insertion sensors can generally not determine the absolute location of the workpiece, but rather only the location relative to a reference location, which makes such a teaching necessary. For this purpose, a workpiece whose location, i.e. the location of the involutes, is determined exactly using the method is preferably measured using an insertion sensor for this purpose and the current location is stored as a reference location. It is then possible with the aid of an insertion sensor taught in this way to bring all further workpieces into the same location or to determine their location relative to the reference location and thus also absolutely.
The present disclosure further relates to a method in accordance with claim 16 for the location-orientated production of a workpiece on a gear-cutting machine, wherein, starting from a separate desired default of the right and/or left base gap half-angle for the workpiece to be produced with respect to a reference direction, one or more desired values are determined for the angle(s) of rotation and/or for the feed(s) of the tool and/or of the workpiece and/or for the crossed-axes angle and/or the axial distance of the two gears. It is conceivable that the calculation provisions for calculating the base gap half-angle in accordance with the above-described method in accordance with the present disclosure for the determination of the location of the involutes are reversed in order to calculate corresponding adjustment movements for the gear-cutting machining starting from a predefined desired position of the involutes. For example, on the basis of predefined base gap half-angles for the desired involute shape of the workpiece, a corresponding desired value for the angle(s) of rotation of the tool/workpiece and/or the feed(s) of the tool/workpiece can be calculated. A corresponding actuation of the machine axes then results in the desired involute shape of the workpiece during the gear-cutting movement.
The reference direction for the base gap half angle can preferably be determined by measurement with a measuring sensor. The calculation of the desired value(s) for the angle(s) of rotation, the feed(s), the axial distance and/or the crossed-axes angle ideally takes place using kinematic chains which describe the relative location between the workpiece and the tool.
The method in accordance with the present disclosure for the location-orientated production can preferably also be carried out combined with the method for the location determination of the involutes.
In addition to the method in accordance with the present disclosure, the present disclosure additionally relates to a gear-cutting machine having a CNC control, wherein the CNC control has corresponding program regulations for carrying out the method in accordance with the present disclosure for the location determination of the involutes and/or the method in accordance with the present disclosure for the location-orientated production or an advantageous embodiment of these methods in accordance with the present disclosure. The gear-cutting machine additionally comprises suitable machine axes for carrying out the required relative movement between the workpiece and the tool as well as corresponding sensors or corresponding detection means to be able to determine the axial changes precisely and to be able to detect the moment of the contact between the workpiece and the tool.
The advantages and properties of the gear-cutting machine in accordance with the present disclosure obviously correspond to those of the corresponding methods in accordance with the present disclosure so that a repeat description will be dispensed with at this point.
Further advantages and properties of the present disclosure will be explained in more detail in the following with reference to a plurality of Figure representations.